The present invention relates to an inverter device, and relates more particularly to an inverter device having a circuit for preventing improper operation and voltage breakdown of a high withstand voltage IC used for drive control of a bridge circuit including switching elements driving a load.
As taught in Japanese Patent Laid-open Publication No. 10-42575, conventional inverter devices have a clamp diode connected between a high voltage reference terminal and low voltage reference terminal of a high withstand voltage IC used for drive controlling switching elements for handling negative surges resulting from line inductance and current variation per unit time, di/dt, when switching a switching element driving a load.
Basic technological premise of this invention, and problems therewith
FIG. 8 is a schematic circuit diagram showing connection of the above-noted clamp diode. It should be noted that FIG. 8 shows only the peripheral circuits of one exemplary high withstand voltage IC, for example, the high withstand voltage IC for switching control of switching elements driving a load connected to the external connection terminal U to which the load is connected.
Clamp diode 102 is connected between high voltage side reference terminal Vs and low voltage side reference terminal VSS of high withstand voltage IC 101; high withstand voltage IC 101 controls operation of switching element 104 connected between external power supply terminal P to which a positive supply voltage is applied, and external terminal U to which a load is connected. The high withstand voltage IC controlling operation of switching element 105 connected between external terminal U and external power supply terminal N to which a negative supply voltage is applied is omitted in this figure.
Voltage V (Vsxe2x88x92VSS) is held by clamp diode 102 to the forward voltage of clamp diode 102 only when a negative potential surge causes voltage V (Vsxe2x88x92VSS) between high voltage side reference terminal Vs and low voltage side reference terminal VSS to become a negative voltage.
However, if the impedance of the load connected to external terminal U is low, heavy current flows when the load is driven, and the negative potential surge reaches several tens of volts, a negative potential greater than or equal to the withstand voltage of the high withstand voltage IC 101. The voltage is applied because of the delay due to the normal recovery time and the V-I characteristic of clamp diode 102 when a heavy current of several hundred amperes, for example, flows. It is therefore not possible for clamp diode 102 alone to sufficiently suppress the negative voltage applied to the high withstand voltage IC 101, resulting in improper operation, and, in some cases, breakdown of high withstand voltage IC 101.
The present invention resolves the above described problem, and an object of this invention is to provide an inverter apparatus preventing breakdown and improper operation of a high withstand voltage IC that controls the switching operation of switching elements for driving a load.
An inverter apparatus according to the present invention includes an inverter circuit part for inverter driving a load. This inverter circuit part has at least a pair of switching elements connected in series in a forward direction between both polarity terminals of a dc supply for supplying power to a load. An inverter drive circuit part is employed for driving each switching element of the inverter circuit part and has at least one high withstand voltage IC wherein the signal level reference potential is different in the input signal and output signal. A clamping circuit part clamps the potential of the low voltage side reference terminal, to which a potential that is a reference for operation of the high withstand voltage IC in the inverter drive circuit part and is a reference for a signal on the low potential side of the high withstand voltage IC is applied, to the high voltage reference terminal to which is applied a reference potential for the high potential-side signal in the high withstand voltage IC. The inverter apparatus also includes a voltage dividing circuit part for voltage dividing a voltage between the low voltage side reference terminal of the high withstand voltage IC in the inverter drive circuit part and the negative electrode of the dc supply.
By thus providing a voltage dividing circuit part for voltage dividing a voltage between the low voltage reference terminal of the high withstand voltage IC and the negative electrode of the dc supply, a negative voltage applied between the high voltage reference terminal and the low voltage reference terminal of the high withstand voltage IC is prevented from going below the minimum rated withstand voltage of the high withstand voltage IC.
The voltage dividing circuit part can also be disposed to each high withstand voltage IC.
Preferably, the voltage dividing circuit part is an element functioning as a voltage dividing resistance connected between the low voltage side reference terminal of the high withstand voltage IC in the inverter drive circuit part and the negative electrode of the dc supply, in which case the voltage dividing circuit part is an element effecting a voltage dividing resistance, such as one resistor or one inductance.
Further preferably, the low voltage side reference terminal of the high withstand voltage IC in the inverter drive circuit part is connected by way of a diode to elements functioning as the clamping circuit part and voltage dividing resistance, and current flows from the voltage dividing resistance in the direction of the low voltage reference terminal of the high withstand voltage IC.
Yet further preferably, the bypass circuit part for bypassing the voltage dividing circuit part is disposed to each voltage dividing circuit part so that high withstand voltage IC operating current output from the low voltage reference terminal flows to the negative electrode of the dc supply.
More specifically, this bypass circuit part is a bypass diode for bypassing the voltage dividing circuit part, and the bypass circuit part comprises one bypass diode.